Random Access Techniques in Beamformed Wireless Communications

1. A method for wireless communication, comprising: transmitting a first random access request to a base station using a first random access resource to initiate a connection establishment with the base station, the first random access resource associated with a first transmission beam of a first set of transmission beams for monitoring system information of the base station; receiving, based at least in part on the connection establishment, configuration information that indicates a second set of transmission beams, wherein the second set of transmission beams includes each transmission beam of the first set of transmission beams and at least an additional transmission beam; transmitting a second random access request to the base station based on the additional transmission beam, wherein the second random access request uses the first random access resource, wherein the first random access request comprises a first MSG 1 transmission and the second random access request comprise a second MSG 1 transmission; and receiving one or both of a first random access response to the second random access request via the first transmission beam and a second random access response to the second random access request via the additional transmission beam.

2. The method of claim 1 , further comprising: monitoring for the first random access response or the second random access response on resources associated with each of the first transmission beam and the additional transmission beam.

3. The method of claim 2 , further comprising: transmitting a third random access message to the base station responsive to the first or second random access response, the third random access message identifying the additional transmission beam is to be used for communications.

4. The method of claim 3 , further comprising: receiving a fourth random access message from the base station via the additional transmission beam.

5. The method of claim 1 , further comprising: identifying the first set of transmission beams to monitor for the system information of the base station; identifying a first set of random access resources for transmission of the first random access request to the base station; and mapping the additional transmission beam to at least the first random access resource.

6. The method of claim 5 , wherein the identifying the first set of transmission beams further comprises: receiving a system information transmission from the base station that indicates the first set of transmission beams, and wherein the first set of random access resources is determined based at least in part on the first set of transmission beams.

7. The method of claim 5 , wherein mapping the additional transmission beam to at least the first random access resource further comprises: determining that the first transmission beam of the first set of transmission beams has a first set of beamforming parameters that are closer to a second set of beamforming parameters of the additional transmission beam than other transmission beams of the first set of transmission beams.

8. The method of claim 1 , wherein the receiving the configuration information further comprises: receiving additional system information indicating that the additional transmission beam is available for communications with the base station.

9. The method of claim 1 , wherein the receiving the configuration information further comprises: receiving an indication of a mapping between a first set of random access resources and the at least one additional transmission beam.

10. The method of claim 9 , wherein the indication of the mapping is received in one or more of a remaining minimum system information (RMSI) from the base station or a radio resource control (RRC) signaling from the base station.

11. The method of claim 9 , wherein the indication of the mapping comprises an explicit indication of a correspondence between each additional transmission beam and a random access resource of the first set of random access resources, or an index value of a predefined indexed set of mappings.

12. A method for wireless communication, comprising: transmitting system information on a first set of transmission beams to at least a first user equipment (UE) for initial system access; configuring a first set of random access resources for transmission of random access requests by one or more UEs, the first set of random access resources including a first random access resource that is associated with a first transmission beam of the first set of transmission beams; receiving a first random access request from the first UE using the first random access resource to initiate a connection establishment with a base station; transmitting, during the connection establishment, configuration information that indicates a second set of transmission beams, wherein the second set of transmission beams includes each transmission beam of the first set of transmission beams and at least a second transmission beam in addition to the first set of transmission beams; mapping the second transmission beam to at least the first random access resource; receiving a second random access request from the first UE using the first random access resource, wherein the first random access request comprises a first MSG 1 transmission and the second random access request comprise a second MSG 1 transmission; transmitting one or both of a first random access response to the second random access request via the first transmission beam and a second random access response via to the second random access request the second transmission beam; and receiving an indication that the second transmission beam is to be used for communications.

13. The method of claim 12 , wherein transmitting the system information comprises: transmitting a synchronization system block (SSB) using each transmission beam of the first set of transmission beams, the SSB including system information that indicates the first set of transmission beams, and wherein the first set of random access resources is determined based at least in part on the first set of transmission beams.

14. The method of claim 12 , wherein transmitting the configuration information further comprises: transmitting additional system information to the first UE indicating one or more additional transmission beams, in addition to the first set of transmission beams, are available for communications.

15. The method of claim 12 , wherein transmitting the configuration information further comprises: transmitting an indication of a mapping between the first set of random access resources and the one or more additional transmission beams.

16. The method of claim 15 , wherein the indication of the mapping comprises an explicit indication of a correspondence between each of the additional transmission beams and a random access resource of the first set of random access resources, or an index value of a predefined indexed set of mappings.

17. The method of claim 12 , further comprising: transmitting the first random access response or the second random access response using each of the first transmission beam and the second transmission beam.

18. The method of claim 17 , further comprising: receiving a third random access message from the first UE responsive to the first or second random access response, wherein the third random access message comprises the indication that the second transmission beam is to be used for communications.

19. The method of claim 12 , further comprising: transmitting a fourth random access message from the base station via the second transmission beam.

20. The method of claim 12 , wherein mapping the second transmission beam to at least the first random access resource further comprises: determining that the first transmission beam of the first set of transmission beams has a first set of beamforming parameters that are closer to a second set of beamforming parameters of the second transmission beam than other transmission beams of the first set of transmission beams.

21. An apparatus comprising: memory storing instructions; and one or more processors in electronic communication with the memory, the one or more processors configured to execute the instructions to cause the apparatus to: transmit a first random access request to a base station using a first random access resource to initiate a connection establishment with the base station, the first random access resource associated with a first transmission beam of a first set of transmission beams for monitoring system information of the base station; receive, based at least in part on the connection establishment, configuration information that indicates a second set of transmission beams, wherein the second set of transmission beams includes each transmission beam of the first set of transmission beams and at least an additional transmission beam; transmit a second random access request to the base station based on the additional transmission beam, wherein the second random access request uses the first random access resource, wherein the first random access request comprises a first MSG 1 transmission and the second random access request comprise a second MSG 1 transmission; and receive one or both of a first random access response to the second random access request via the first transmission beam and a second random access response to the second random access request via the additional transmission beam.

22. The apparatus of claim 21 , the one or more processors configured to further execute the instructions to cause the apparatus to: monitor for the first random access response or the second random access response on resources associated with each of the first transmission beam and the additional transmission beam; and transmit a third random access message to the base station responsive to the random access response, the third random access message identifying the additional transmission beam is to be used for communications.

23. The apparatus of claim 22 , the one or more processors configured to further execute the instructions to cause the apparatus to: receive a fourth random access message from the base station via the additional transmission beam.

24. The apparatus of claim 21 , the one or more processors configured to further execute the instructions to cause the apparatus to: identify the first set of transmission beams to monitor for the system information of the base station; identify a first set of random access resources for transmission of the first random access request to the base station; and map the additional transmission beam to at least the first random access resource.

25. The apparatus of claim 24 , wherein the one or more processors cause the apparatus to map the additional transmission beam to at least the first random access resource by determining that the first transmission beam of the first set of transmission beams has a first set of beamforming parameters that are closer to a second set of beamforming parameters of the additional transmission beam than other transmission beams of the first set of transmission beams.

26. The apparatus of claim 21 , wherein the one or more processors cause the apparatus to receive the configuration information by receiving additional system information indicating that the additional transmission beam is available for communications with the base station.

27. The apparatus of claim 21 , wherein the one or more processors cause the apparatus to receive the configuration information by receiving an indication of a mapping between a first set of random access resources and the at least one additional transmission beam.

28. The apparatus of claim 21 , wherein the one or more processors cause the apparatus to map the second transmission beam to at least the first random access resource by determining that the first transmission beam of the first set of transmission beams has a first set of beamforming parameters that are closer to a second set of beamforming parameters of the second transmission beam than other transmission beams of the first set of transmission beams.

29. An apparatus comprising: memory storing instructions; and one or more processors in electronic communication with the memory, the one or more processors configured to execute the instructions to cause the apparatus to: transmit system information on a first set of transmission beams to at least a first user equipment (UE) for initial system access; configure a first set of random access resources for transmission of random access requests by one or more UEs, the first set of random access resources including a first random access resource that is associated with a first transmission beam of the first set of transmission beams; receive a first random access request from the first UE using the first random access resource to initiate a connection establishment with a base station; transmit, during the connection establishment, configuration information that indicates a second set of transmission beams, wherein the second set of transmission beams includes each transmission beam of the first set of transmission beams and at least a second transmission beam in addition to the first set of transmission beams; map the second transmission beam to at least the first random access resource; receive a second random access request from the first UE using the first random access resource, wherein the first random access request comprises a first MSG 1 transmission and the second random access request comprise a second MSG 1 transmission; transmit one or both of a first random access response to the second random access request via the first transmission beam and a second random access response via to the second random access request the second transmission beam; and receive an indication that the second transmission beam is to be used for communications.

30. The apparatus of claim 29 , the one or more processors configured to further execute the instructions to cause the apparatus to: transmit the first random access response or the second random access response using each of the first transmission beam and the second transmission beam; and receive a third random access message from the first UE responsive to the first random access response or the second random access response, wherein the third random access message comprises the indication that the second transmission beam is to be used for communications.